This invention relates to a self-cleaning filter assembly for use in a solenoid-actuated valve of the type having a fluid pressure-operated diaphragm to control opening and closing of the valve. More specifically, the self-cleaning filter assembly of this invention comprises an improvement over the self-cleaning filter assembly disclosed and claimed in U.S. Pat. No. 4,081,171.
In U.S. Pat. No. 4,081,171, a self-cleaning filter assembly is disclosed for filtering control fluid in a solenoid-actuated valve including a pressure-responsive diaphragm movable to open and close the valve. This filter assembly comprises a filter element of mesh screen for filtering dirt, grit, and the like from the control fluid, and a brush for sweeping accumulated filtered matter from the filter element. The filter element and the brush are mounted for movement relative to each other, and one of the filter element and the brush is movable with the diaphragm whereby the brush sweeps the surface of the filter element each time the valve is opened or closed.
The filter assembly set forth in U.S. Pat. No. 4,081,171, however, includes a variety of disadvantages which have limited its commercial utility. For example, the bristles of the brush are capable of engaging only a relatively small total surface area of the mesh screen filter element, resulting in an inability of the brush to remove thoroughly the filtered matter from the filter element. This relatively low cleaning effectiveness of the brush is further reduced by a tendency of the bristles and the mesh screen filter element to flex away from each other as filtered matter builds up on the surface of the filter element. Moreover, the mesh screen filter element is formed from a woven network of small wires to define a plurality of filter openings each having an initially converging cross section. Small particles of dirt or grit can therefore be forced by the brush into the converging openings to become trapped therein, and once trapped, the flexible bristles on the brush are incapable of dislodging the particles to unclog the filter element either by sweeping them free or by forcing them through the filter openings. Still further, the brush bristles tend to become caught in these filter openings, or alternately, to deflect to a set position with substantially reduced cleaning engagement with the filter element. When the filter assembly is used for filtering water, both the brush and the woven-textured filter element provide a large number of small cavities highly susceptible to growth of algae, resulting in a sliming over of both the brush and the filter element.
The present invention overcomes the problems and disadvantages of the prior art by providing an improved self-cleaning filter assembly for use with solenoid-actuated valves. The invention includes an improved filter element in cooperation with an improved cleaning element to provide a self-cleaning filter assembly for thoroughly cleaning filterd matter from the filter element and which is not susceptible to clogging or to the growth of algae.